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Alert Notice 621: Optical monitoring of NSV 24045 = HD 163296

March 15, 2018: Evan A. Rich (Ph.D. candidate, University of Oklahoma), and Drs. John Wisniewski (University of Oklahoma), John Tobin (University of Oklahoma), Carol Grady (Goddard Space Flight Center), and Mike Sitko (University of Cincinnati) have requested AAVSO assistance in monitoring the bright (6.9 V) Young Stellar Object NSV 24045 (HD 163296) from now through September 2018.

They write: "HD 163296 is a prototypical Young Stellar Object with a A1V spectral classification and an associated large dust and gas disk. It is common for these objects to be associated with Herbig-Haro knots (HH knots) which are clumps of dust and gas that have been launched from the disk around the star (< 3 AU) and ejected from the system along the polar axis of the star. Ellerbroek et al. 2014 used these HH knots as 'fossils' and traced back when the knots were first ejected from the system. They found a 16 year periodicity of the knot ejections. The last HH knot is thought to have occurred in 2002 meaning that it is likely for the next HH knot ejection to happen within 2018.

"We want to detect the predicted 2018 ejection of the HH knot in order to confirm the Ellerbroek et al. 2014 prediction and investigate the mechanisms causing the knots to eject periodically. In order to accomplish this goal, we need a contemporaneous multi-wavelength observations of HD 163296 on timescales between a week and a month.

"[The following observations are scheduled:]
- Very Large Array, to detect the radio radiation and monitor the object...When the knot is launched from the disk, the high velocity of the dust and gas interacting with the interstellar medium will emit cyclotron radiation which is detectable at radio wavelengths.
- Apache Point Observatory's Triplespec instrument, to detect changes in the near-IR. Dust traveling between the star and the observer is thought to radiate thermally causing a near-IR excess of flux.
- Hubble Space Telescope STIS coronagraphic imaging...to resolve the dust disk around the star. We will look for non-symmetric features that are most likely caused by shadowing either by the disk itself or by dust obscuring the star.

"What we are missing is optical photometry. Dust that is launched from the knot will also cause the star to dim in the optical. We need contemporaneous optical observations that will be compared to our radio and near-IR observing campaigns to fully constrain the mechanisms that are causing the variability in HD 163296."

Beginning now and continuing through September 2018, UBVRI or equivalent photometry is requested, with a cadence range of one observation per filter per night to one observation per filter per week. NSV 24045 has a V range of magnitude 6.8-7.9, with an average magnitude of 6.9 V.

Coordinates (2000.0): R.A. 17 56 21.29 Dec. -21 57 21.9

Charts with a comparison star sequence for NSV 24045 may be plotted using the AAVSO Variable Star Plotter (VSP). Observers will need to create a 'b' or 'c' scale chart; it is suggested that observers use the comparison stars to the South and Southeast of the target.

Please submit observations to the AAVSO International Database using the name NSV 24045.